Multiple complex developmental disorder (MCDD): Did we throw the baby out with the bathwater too fast? A systematic review

Background Multiple complex developmental disorder (MCDD) manifests as early-onset impairment across different domains. Although it could appear as a transitional condition between autism and childhood-onset schizophrenia, interest in MCDD has progressively waned. This study attempts to discern MCDD current relevance to avoid "throwing the baby out with the bathwater" too fast.Methods All available studies published up to January 2024 were retrieved and evaluated following on the PRISMA guidelines for systematic reviews using the term "multiple complex developmental disorder" or "MCDD", without any filter for study design nor year of publication.Results Only 16 studies were included and analyzed. Overall, a variable heterogeneity was observed in terms of country of investigation, study design, and clinical groups. Most of the included studies explored the construct of MCDD in developmental age, comparing MCDD mostly with autistic patients, and observing how the former group had higher levels of paranoia, illusions, and psychotic thoughts, whereas the latter showed more frequently difficulties in social interactions and stereotypical behaviors.Conclusion Overall, these results showed how progressive changes in diagnostic criteria over time led MCDD to be abandoned as nosographic construct, leaving perhaps a diagnostic void between autism and psychotic disorders that needs to be further studied. A systematic review on the Multiple Complex Developmental Disorder (MCDD): a forgotten diagnosis between autism and schizophrenia.Multiple complex developmental disorder (MCDD) seems to have covered in the past years a grey area between autism and schizophrenia with onset in childhood, as it includes some symptoms usually observed in the former condition (dysregulation of affectivity, impairment in social interactions) and some in the latter (behavioral disorganization and thought problems, such as bizarre ideas, paranoid concerns, or magical thinking). This systematic review aims at summarizing the published scientific literature about the MCDD, wondering whether it is worth reconsidering its current relevance. In over 20 years (from 1993 to 2015) only 16 studies dealt with the topic, with a great heterogeneity in terms of country of investigation, study design, and clinical groups. Most of the studies compared MCDD with autism, trying to outline clinical differences between the two conditions. This information may help child psychiatrists and other mental health professionals reflect about those "weird" young patients they usually visit in their practice, and whose diagnosis appears not centered because they do not completely fulfill the diagnostic criteria of autism or schizophrenia.